Sex Differences in the Rate, Timing, and Principal Diagnoses of 30-Day Readmissions in Younger Patients with Acute Myocardial Infarction

BACKGROUND: Young women (<65 years) experience a 2- to 3-fold greater mortality risk than younger men after an acute myocardial infarction. However, it is unknown whether they are at higher risk for 30-day readmission, and if this association varies by age. We examined sex differences in the rate, timing, and principal diagnoses of 30-day readmissions, including the independent effect of sex following adjustment for confounders. METHODS AND RESULTS: We included patients aged 18 to 64 years with a principal diagnosis of acute myocardial infarction. Data were used from the Healthcare Cost and Utilization Project-State Inpatient Database for California (07-09). Readmission diagnoses were categorized by using an aggregated version of the Centers for Medicare and Medicaid Services' Condition Categories, and readmission timing was determined from the day after discharge. Of 42,518 younger patients with acute myocardial infarction (26.4% female), 4775 (11.2%) had at least 1 readmission. The 30-day all-cause readmission rate was higher for women (15.5% versus 9.7%, P<0.0001). For both sexes, readmission risk was highest on days 2 to 4 after discharge and declined thereafter, and women were more likely to present with noncardiac diagnoses (44.4% versus 40.6%, P=0.01). Female sex was associated with a higher rate of 30-day readmission, which persisted after adjustment (hazard ratio, 1.22; 95% confidence interval, 1.15-1.30). There was no significant interaction between age and sex on readmission. CONCLUSIONS: In comparison with men, younger women have a higher risk for readmission, even after the adjustment for confounders. The timing of 30-day readmission was similar in women and men, and both sexes were susceptible to a wide range of causes for readmission.